Ruthenium dihydrogen complex for C-H activation: Catalytic H/D exchange under mild conditions

Catalytic H/D-exchange reactions were studied with [Ru(dtbpmp) (η²-H₂)(H)₂] (1) as catalyst. Under mild reaction conditions (25-75°C) a wide range of arenes and olefins undergo H/D exchange with [D₆]benzene. A preference for protons at sp ² carbons was observed with conversions up to >90% and significant regioselectivity in certain cases. For more reaction insights NMR-based kinetic studies were performed with naphthalene as substrate, revealing an activation energy of 15.8 kcal mol^-1 for the H/D exchange at the β-position. Furthermore, the key steps of the reaction mechanism were investigated by means of DFT calculations for both model complexes (PMe ₂ donor sites) and real catalysts (PtBu₂ donor sites). The calculations resulted in Gibb's free activation energies in the range of 10-16 kcal mol^-1, indicating H/D exchange at the β-position of naphthalene to be clearly favoured over the α-position, which is in full accordance with the experimental observations.